1. Field of the Invention
The present invention relates to a tuning fork type vibration element comprising two arms which form a tuning fork and vibrate torsionally, and a base which supports these two arms, and to a tuning fork type vibration gyro comprising such a tuning fork type vibration element so as to detect the rotation angular velocity.
2. Description of the Prior Art
Gyroscope has been used as means for identifying the position of the moving object such as airplane, large vessel, space satellite, and the like. Recently, it is utilized for detecting vibration of apparatus such as car navigation, VTR, still camera, and the like in civil field.
Among these gyroscopes, a vibration gyro made by utilizing a piezoelectric element has been in practical use. The piezoelectric vibration gyro is made by utilizing the principle that, when a rotation angular velocity is exerted to an object which is vibrating at a predetermined rate, Coriolis force is formed in the orthogonal direction to the vibration. Various types of such piezoelectric vibration gyro have been proposed. Above all, recently, research and development of tuning fork type vibration gyro utilizing the piezoelectric monocrystal has been made vigorously, seeking for the downsizing and shortening of gyros.
FIG. 1 is a perspective view of the general structure of a tuning fork type vibration element 1 used for a tuning fork type vibration gyro. The tuning fork type vibration element 1 includes two arms 2, 3 of rectangular parallelepiped form having square bottom face, and a base 4 of rectangular parallelepiped form supporting the arms 2, 3. These arms 2, 3 and the base 4 are formed in one-piece by a piezoelectric monocrystal such as LiTaO.sub.3, LiNbO.sub.3, or the like. The tuning fork type vibration element 1 having this structure is attached to an object whose rotation angular velocity is supposed to be detected, and the arms 2, 3 are vibrated torsionally. When the rotation angular velocity is exerted to the object, an electromotive force generated by Coriolis force which is formed in the orthogonal direction to the torsional vibration is detected, so as to detect the rotation angular velocity of the object.
FIG. 2 shows how the tuning fork type vibration element 1 vibrates torsionally. In FIG. 2, the arrows indicate the direction of the torsional vibration, the positions of the arms 2, 3 before and after the torsional vibration are indicated by dot lines and solid lines, respectively. When the torsional vibration shown in FIG. 2 is generated, the vibration causes not only the arms 2, 3, but also the base 4 to rotate. In this case, there is a problem that the support unit (node unit) of the tuning fork type vibration element 1 supports only the center of the rotation, so that the support for the external vibration is weakened. On the other hand, if the support is reinforced, there is a problem that the Q value is decreased.
In order to solve these problems, the tuning fork type vibration element 1 having the structure shown in FIG. 3 has been proposed. The tuning fork type vibration element 1 has an H-type structure including two arms 12, 13 which are provided on the opposite side of the base 4 in addition to the arms 2, 3. In the tuning fork type vibration element 1 having this H-type structure, the rotation of the base 4 is prevented by generating torsional vibration by each pair of the arms 2, 3 and the arms 12, 13, thereby forming double torsional conditions with two torsional vibrations. As a result, the support for the external vibration is facilitated, thereby enhancing the Q value of the torsional vibration.
However, according to the H-type tuning fork type vibration element 1 shown in FIG. 3, there is a problem that the arms 12, 13 lengthen the entire length of the vibration element 1, failing to meet the demand for a smaller and shorter tuning fork type vibration element gyro. There is another problem that balancing the upper arms 2, 3 and the lower arms 12, 13 makes the processing of the arms hard and lowers the productivity, thereby leading to increase in the processing cost and the component cost.